Longitudinal plunging unit with a hollow profiled journal

ABSTRACT

A longitudinal plunging unit ( 11 ) for torque transmitting purposes in a shaft assembly, comprising an outer profiled sleeve ( 21 ) having circumferentially distributed, inner, longitudinally extending first ball grooves ( 22 ) to be connected to a first attachment part, a profiled journal ( 31 ) positioned inside the outer profiled sleeve ( 21 ) and having circumferentially distributed, outer, longitudinally extending second ball grooves ( 32 ) to be connected to a second attachment part, groups of balls ( 41 ) arranged in pairs of first and second ball grooves ( 22, 32 ), and a sleeve-shaped ball cage ( 42 ) which is positioned in the annular space between the profiled sleeve ( 21 ) and the profiled journal ( 31 ) and which fixes the groups of balls ( 41 ) in their respective positions relative to one another. The profiled journal ( 31 ) is a hollow journal comprising a material with a substantially uniform wall thickness with a maximum deviation of ±15%.

TECHNICAL FIELD

The invention relates to a longitudinal plunging unit for torquetransmitting purposes in a shaft assembly. The unit includes an outerprofiled sleeve having circumferentially distributed, inner,longitudinally extending first ball grooves to be connected to a firstattachment part, a profiled journal positioned inside the outer profiledsleeve and having circumferentially distributed, outer, longitudinallyextending second ball grooves to be connected to a second attachmentpart, groups of balls arranged in pairs of first and second ballgrooves, and a sleeve-shaped ball cage which is positioned in theannular space between the profiled sleeve and the profiled journal andwhich fixes the groups of balls in their respective positions relativeto one another.

BACKGROUND OF THE INVENTION

Such axial plunging units serve the transmission of torque in shaftassemblies which, when in operation, are subject to changes in length.These changes in length in a motor vehicle, for example, are caused bymovements of one of the attachment parts due to compression and reboundactions. To the extent that reference is made to shaft assemblies, it isalso possible for the latter to be formed largely by the longitudinalplunging unit itself which is then directly connected to attachmentpieces such as welded-on flanges and slipped-on hubs.

When a profiled sleeve is displaced relative to a profiled journal whileunder torque, the rolling movement of the balls in the inner and outerball grooves is substantially free from any sliding friction, so thatthe balls and thus the ball cage with all the balls cover half therelative plunging distance between the two parts. This permits thechange in length of the longitudinal plunging unit to be of alow-friction nature. At the ends of the plunging path, axial stops forthe ball cage or for the balls have to be provided in the profiledsleeve or on the profiled journal. Under normal operating conditions,the ball cage should preferably not reach the axial stops, but it shouldbe freely displaceable on the plunging path specified by the design,thus avoiding any sliding friction of the balls in the grooves.

Assemblies of this type are used in torque-transmitting shafts,especially driveshafts which—for compensating for tolerances in thedistance between the attachment parts during assembly and/or forcompensating changes in the distances between the attachment parts, suchas joints, in operation—require low-friction plunging conditions. Whenin operation and during the transmission of torque, such driveshaftssuffer from a problem in that the inter-engaging portions of theprofiled sleeve and of the profiled journal are, by necessity, subjectto torsion in the regions of the ball grooves.

As a result of the torsional movements of the profiled sleeve and of theprofiled journal during the transmission of torque, there can occuruneven load conditions at the balls in the different cross-sectionalplanes. This adversely affects smooth and easy movability and can leadto early failure. In order to avoid this, it is desirable for both partsto feature a high degree of stiffness.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide alongitudinal plunging unit of the foregoing type which combines a highdegree of strength with a lightweight design.

The present invention provides a profiled journal produced as a hollowjournal. This measure permits the greatest savings in respect of weightand material at the profiled journal, which savings have so far not beenpossible. In particular, the profiled journal comprises a material witha substantially uniform wall thickness, such as with a maximum deviationin wall thickness of ±15%. The reduction in weight reduces the risk ofbuckling of light-weight high-speed hollow shafts. According to apreferred embodiment, in the region adjoining the second ball grooves,towards the second attachment part, the profiled journal changesintegrally into a tubular cylindrical portion whose outer diameter isapproximately the same size as an enveloping circle around the secondprofiled grooves.

According to a preferred embodiment the profiled sleeve, too, comprisesa material of substantially the same wall thickness with a maximumdeviation in wall thickness of ±15%. The profiled sleeve, in the regionadjoining the first ball grooves, towards the first attachment part,changes integrally into a first cylindrical projection and, in theregion adjoining the first ball grooves, towards the second attachmentpart, changes integrally into a second cylindrical projection. The twocylindrical projections mentioned improve the dimensional stiffness ofthe profiled sleeve. During the production of the profiled sleeve, thetwo cylindrical projections can be produced particularly easily by beingformed out of a tubular member. The first cylindrical projection at theattachment end can be connected in an easy way to an adjoining shafttube, either via an abutting connection or by being inserted into orslid onto same. The second cylindrical projection at the insertion end,which second cylindrical projection points towards the attachment partof the profiled journal can be provided in the form of a seal and stopfor the balls held in the cage. If the second cylindrical projection hasa greater inner diameter than the cross-section of the ball grooves, itis capable of accommodating sealing and stopping means by way of a pressfit.

According to a preferred embodiment, the inner diameter of the firstcylindrical projection is greater than an enveloping circle around theballs held in a functionally accurate or operationally accurate way inthe cage. This makes it possible to insert the ball cage with the ballsfrom the attachment end. Optionally, a stopping mechanism for the cagecan be inserted into the first cylindrical projection to prevent thecage from being disconnected from the profiled journal inside theprofiled sleeve.

The profiled sleeve, in the region of the first ball grooves, ispreferably provided with a metal armouring which comprises a high wearstrength and a uniform wall thickness.

Both the profiled journal and the profiled sleeve can be produced from atube by way of deformation, and the profiled sleeve provided with anarmouring can be produced from a tube provided with an armouring sleevewhich was inserted with a press fit. A radial material pre-tensionbetween the profiled sleeve and the armouring sleeve has astrength-increasing effect. Analogously, the profiled journal can beprovided with an armouring in the region of the ball grooves, whicharmouring can comprise an armouring sleeve which is slid on to a tubeand which, together with the tube, is deformed into the profiledjournal.

Other advantages and features of the invention will also become apparentupon reading the following detailed description and appended claims, andupon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention.

In the drawings:

FIG. 1 is a longitudinal section through an axial plunging unit inaccordance with the invention, in a first embodiment.

FIG. 2 is a longitudinal section through an axial plunging unit inaccordance with the invention, in a second embodiment.

FIG. 3 is a longitudinal section through the profiled sleeve accordingto FIG. 1 in the form of a detail.

FIG. 4 is a cross-section through the profiled sleeve according to FIG.3.

FIG. 5 is a longitudinal section through a profiled sleeve similar toFIG. 3 in a modified embodiment in the form of a detail.

FIG. 6 is a cross-section through the profiled sleeve according to FIG.5.

FIG. 7 is a longitudinal section through the profiled journal of theunits according to FIGS. 1 and 2 in the form of a detail.

FIG. 8 is a cross-section through the profiled journal according to FIG.7.

FIG. 9 is a longitudinal section through a profiled journal similar tothat of FIG. 7 in modified embodiment in the form of a detail.

FIG. 10 is a cross-section through the profiled journal according toFIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 will be described jointly below. They each show alongitudinal section through an inventive axial plunging unit 11 whichcomprises a profiled sleeve 21, a profiled journal 31, groups of torquetransmitting balls 41 and a sleeve-shaped ball cage 42. On the right,the profiled sleeve 21 can be connected to a first attachment part, suchas a tubular shaft. On the left, the profiled journal 31 can beconnected to a second attachment part, such as a slid-on jointcomponent. The profiled sleeve 21 comprises a material with asubstantially uniform wall thickness and, on its inside, compriseslongitudinally extending ball grooves 22. At the end of the firstattachment part, the profiled sleeve 21 is expanded towards a firstcylindrical projection 23 whose inner diameter is greater than anenveloping circle around the ball 41 in its design-related functionallyaccurate position as held by the cage 42. The ball cage can thus beinserted from the right through the first cylindrical projection 23 intothe region of the first ball grooves 22. The cylindrical projection 23is suitable for connecting an adjoining tubular shaft by but welding or,optionally, for inserting a shaft which can stop at the run-out portions24 of the ball grooves. Towards the second attachment piece, theprofiled sleeve comprises a second cylindrical projection 25 whose innerdiameter is reduced relative to the region of the ball grooves 22. Thecylindrical projection 25 increases the dimensional stiffness of theprofiled tube 21 at its free end. It should be noted at this point that,like the first cylindrical projection 23, the second cylindricalprojection 25 can be increased in size relative to the groove portion.This would make it easier to receive sealing means with a sealingfunction relative to the profiled journal 31. The profiled journal 31also comprises a material with a substantially uniform wall thicknessand includes second ball grooves 32 on its outside. At the end of theball groove region, the profiled journal 31 changes into a cylindricalportion 33 whose outer diameter corresponds to an enveloping circlearound the second ball grooves 32. Said cylindrical portion 33 isfollowed by a portion 34 with a greater wall thickness and with splines35 and with a securing groove 36 whose outer diameter does not exceedthat of the cylindrical portion 33. In this way, the profiled journal 31can be inserted from both directions into the profiled sleeve 21. At thefree end of the ball groove region, the cross-section of the profiledjournal 31 is uniform. The specification that the profiled sleeve andthe profiled journal should comprise a material with a substantiallyuniform wall thickness primarily concerns the longitudinal portions ofthe first ball grooves 22 and of the second ball grooves 32. However,this can also apply to the cylindrical projections 23, 25 and thecylindrical portion 33, but not necessarily to the portion 34 at theprofiled journal.

A slight difference between the two embodiments according to FIGS. 1 and2 is shown wherein, because of a different diameter of the secondcylindrical projection 25 in the first embodiment according to FIG. 1,the ball cage 42 will stop at the transition to the second cylindricalprojection 25, whereas in the second embodiment according to FIG. 2, thefirst balls 41 will stop against the ball groove run-out portions 26 atthe transition to the second cylindrical projection 25.

FIG. 3 shows the profiled sleeve 21 according to FIG. 1 in the form of adetail. Identical details have been given the same reference numbers. Tothat extent, reference is made in full to the description of same.

FIG. 4 shows the profiled sleeve according to FIG. 3 in across-sectional view. It is possible to see a substantially circularbasic shape with formed-out ball grooves 22. In particular, thiscross-sectional shape can be obtained by forming it out of an originallyround tube with a uniform wall thickness. The forming operation can takeplace by drawing the tube in the longitudinal direction over a mandrelthrough a die or by continuous hammering over a core. The final wallthickness measured perpendicularly relative to a tangent in each surfacepoint in the cross-section (on the inside or outside) is allowed tofluctuate within the range of ±15% with reference to a mean value.

FIG. 5 shows a profiled sleeve 21′ in a slightly modified embodimentwhich is largely identical to that shown in FIG. 3. Identical detailshave been given the same reference numbers. To that extent, reference isagain made to the description of FIG. 1. In the region of the first ballgrooves 22, there can be seen an armouring 27 which serves to formwear-resistant running grooves. The armouring is preferably producedfrom a sleeve which, prior to the forming operation, is slid into acircular tube, held by a press fit and, together with the circular tube,is subjected to one of the above-mentioned forming processes.

FIG. 6 shows the profiled sleeve 21′ in a cross-sectional view, and itcan be seen that the armouring 27 also has a substantially uniformthickness. The total thickness, again measured perpendicularly relativeto tangents in each surface point in the cross-section (on the outsideor inside), again should be allowed to vary within the range of ±15%with reference to a mean value.

FIG. 7 shows the profiled journal 31 of the unit according to FIGS. 1and 2 in the form of a detail. Identical details have been given thesame reference numbers. To that extent, reference is made to thedescription of FIGS. 1 and 2.

FIG. 8 shows the profiled journal according to FIG. 7 in across-sectional view. Again, there is shown a basic shape of a circulartube into which the individual ball grooves 32 have been formed. Again,the preferred method of production is deforming a circular tube bydrawing or round hammering. In this case, too, the uniform wallthickness described in connection with the profiled sleeve can beallowed to vary within a range of ±15% with reference to a mean value,in each case measured perpendicularly relative to the wall length, asdescribed above.

FIG. 9 shows a profiled journal 31′ in a slightly modified embodimentwhich largely corresponds to that shown in FIG. 7. Identical detailshave been given the same reference numbers. To that extent, reference ismade to the description of FIGS. 7, 1 and 2. In the region of the secondball grooves 32 it is possible to identify an armouring 37 which servesto form wear-resistant running grooves. The armouring is preferablyproduced from a sleeve which is slid on to a circular tube, secured by apress-fit and, jointly with the circular tube, is subjected to adeformation process.

FIG. 10 shows the profiled journal 31′ in a cross-sectional view; italso shows the armouring 37 with a substantially uniform wall thickness.The total thickness is again measured perpendicularly to the tangents ineach surface point in the cross-section (on the outside or inside) and,in this case, too, it can be allowed to vary within a range of ±15% withreference to a mean value.

From the foregoing, it can be seen that there has been brought to theart a new and improved longitudinal plunging unit with a hollow profiledjournal. While the invention has been described in connection with oneor more embodiments, it should be understood that the invention is notlimited to those embodiments. Thus, the invention covers allalternatives, modifications, and equivalents as may be included in thespirit and scope of the appended claims.

1. A longitudinal plunging unit (11) for torque transmitting purposes ina shaft assembly, comprising: an outer profiled sleeve (21) havingcircumferentially distributed, inner, longitudinally extending firstball grooves (22), said outer profiled sleeve adapted to be connected toa first attachment part; a profiled journal (31) positioned inside saidouter profiled sleeve (21) and having circumferentially distributed,outer, longitudinally extending second ball grooves (32), said profiledjournal adapted to be connected to a second attachment part, and whereinsaid profiled journal (31) is a hollow journal and with a substantiallyuniform wall thickness and a maximum deviation in wall thickness of±15%; groups of balls (41) arranged in pairs of the first and secondball grooves (22, 32); and a sleeve-shaped ball cage (42) positioned inan annular space between the profiled sleeve (21) and the profiledjournal (31) and which fixes the groups of balls (41) in theirrespective positions relative to one another.
 2. A unit according toclaim 1, wherein, in a region adjoining the second ball grooves (32),towards the second attachment part, the profiled journal (31) changesintegrally into a tubular cylindrical portion (33).
 3. A unit accordingto claim 2 wherein an outer diameter of the tubular cylindrical portion(33) is approximately the same size as an enveloping circle around across-section of the profiled journal.
 4. A unit according to claim 1,wherein at least one of the profiled journal (31) and the profiledsleeve (21) comprise a two-layer material with an armouring (27) with ahigh wear strength for the ball grooves (22, 32).
 5. A unit according toclaim 2, wherein at least one of the profiled journal (31) and theprofiled sleeve (21) comprise a two-layer material with an armouring(27) with a high wear strength for the ball grooves (22,32).
 6. A unitaccording to claim 3, wherein at least one of the profiled journal (31)and the profiled sleeve (21) comprise a two-layer material with anarmouring (27) with a high wear strength for the ball grooves (22, 32).7. A unit according to claim 1, wherein the profiled sleeve (21)comprises a material with a substantially uniform wall thickness with amaximum deviation in wall thickness of ±15% and wherein, in a regionadjoining the first ball grooves (22), towards the first attachmentpart, the profiled sleeve (21) changes integrally into a firstcylindrical projection (23) and, in a region adjoining the first ballgrooves (22), towards the second attachment part, the profiled sleeve(21) changes integrally into a second cylindrical projection (25).
 8. Aunit according to claim 2, wherein the profiled sleeve (21) comprises amaterial with a substantially uniform wall thickness with a maximumdeviation in wall thickness of ±15% and wherein, in a region adjoiningthe first ball grooves (22), towards the first attachment part, theprofiled sleeve (21) changes integrally into a first cylindricalprojection (23) and, in a region adjoining the first ball grooves (22),towards the second attachment part, the profiled sleeve (21) changesintegrally into a second cylindrical projection (25).
 9. A unitaccording to claim 3, wherein the profiled sleeve (21) comprises amaterial with a substantially uniform wall thickness with a maximumdeviation in wall thickness of ±15% and wherein, in a region adjoiningthe first ball grooves (22), towards the first attachment part, theprofiled sleeve (21) changes integrally into a first cylindricalprojection (23) and, in a region adjoining the first ball grooves (22),towards the second attachment part, the profiled sleeve (21) changesintegrally into a second cylindrical projection (25).
 10. A unitaccording to claim 7, wherein an inner diameter of the first cylindricalprojection (23) is greater than an enveloping circle around the balls(41) held operationally in the cage (42).
 11. A unit according to claim8, wherein an inner diameter of the first cylindrical projection (23) isgreater than an enveloping circle around the balls (41) heldoperationally in the cage (42).
 12. A unit according to claim 9, whereinan inner diameter of the first cylindrical projection (23) is greaterthan an enveloping circle around the balls (41) held operationally inthe cage (42).
 13. A unit according to claim 7, wherein an innerdiameter of the second cylindrical projection (25) is less than anenveloping circle around the balls (41) held operationally in the cage(42).
 14. A unit according to claim 10, wherein an inner diameter of thesecond cylindrical projection (25) is less than an enveloping circlearound the balls (41) held operationally in the cage (42).
 15. A unitaccording to claim 7, wherein an inner diameter of the secondcylindrical projection (25) is only insubstantially greater than anenveloping circle around a cross-section of the profiled journal.
 16. Aunit according to claim 13, wherein an inner diameter of the secondcylindrical projection (25) is only insubstantially greater than anenveloping circle around a cross-section of the profiled journal.
 17. Aunit according to claim 14, wherein an inner diameter of the secondcylindrical projection (25) is only insubstantially greater than anenveloping circle around a cross-section of the profiled journal.
 18. Aunit according to claim 15, wherein an inner diameter of the secondcylindrical projection (25) is only insubstantially greater than anenveloping circle around a cross-section of the profiled journal.